1. Field of the Invention
This invention relates to novel polyurethane polymers and is more particularly concerned with elastomeric polyurethane-polyurea polymers.
2. Description of the Prior Art
Polyurethane polymers and elastomers prepared from high molecular weight polyols and organic polyisocyanates and extended with low molecular weight polyols, particularly diols, have been known in the art for a long time; see U.S. Pat. No. 2,948,691, and Polyurethane Chemistry and Technology, Part II by J. H. Saunders and K. C. Frisch, Chapter IX, 1964, Interscience Publishers, New York, N.Y. for typical background art.
Polyurethane elastomer properties have been varied in numerous ways by adjusting such parameters as reactant functionality, type of isocyanate or polyol, and, very importantly, by adjusting the amount and the type of extender employed. If an organic polyamine is used as an extender then the resulting polymer will contain polyurea linkages along with the polyurethane.
In some applications, particularly cast elastomers, it is desirable to have slow acting systems. Contrastingly, with the advent of reaction injection molding (RIM) techniques it became desirable to have fast acting systems. Therefore, it is not surprising that there are many different aromatic diamines known in the art ranging typically from the slow methylenebis(o-chloroaniline), to the intermediate polymethylene polyphenylamine, to the very fast methylenebis(aniline). Many different types of substituent groups have been introduced into the aromatic ring to vary the reaction speed of the polymer forming process; see the art cited above.
When polyurethane-polyurea forming ingredients are deposited or otherwise injected into a mold cavity, it is essential that a careful balance of polymer gel time versus the molded part size be maintained. A fast enough gel time is necessary so that good polymer formation along with quick demold time is possible. At the same time, the gel cannot be so fast that polymer gelation is occurring on the mold walls or floor while ungelled reactants are still entering the mold. Accordingly, the polyurethane-polyurea polymer must have suitable reaction profiles which can be varied or adjusted to meet particular needs.
The use of polyamines including diamines and amines of functionality greater than two, as extenders in elastomeric polyurethanes, is well known in the art. For examples of the application of the latter type of extenders see U.S. Pat. Nos. 3,575,896 and 4,048,105. For examples of the application of diamines as extenders see U.S. Pat. Nos. 3,267,050, 3,428,610, 3,591,532, 3,681,290, 3,736,350, 3,794,621, 3,808,250, and 3,817,940; German Patent Application No. 2,635,400; and British Pat. Nos. 1,408,943, and 1,534,258.
The use of mixed extenders comprised of the polyamines with low molecular weight diols and triols has also been prevalent in the art. In this regard, note particularly the German Patent Application No. 2,635,400 and British Pat. No. 1,534,258.
Generally speaking, the use of polyamines as extenders gives rise to polymer products, particularly products molded with compact skins, that are characterized by excellent physical properties such as impact, tensile, modulus properties, and tear strengths in a given hardness range. At the same time, the use of unhindered polyamine extenders leads to reaction and processing times that are much faster than the reaction times of the diol extended polymers. The aromatic polyamines are generally preferred with the diamines being the most preferred types.
British Pat. No. 1,534,258 discloses the use of certain types of aromatic diamines as extenders including both unsubstituted and substituted amines with the latter being preferred in the RIM preparation of polyurethanepolyureas. The reference also discloses the use of extenders in which up to 50 percent by weight of the diamine is replaced by primary hydroxyl diol extenders. The disclosed polymers are characterized by very fast reaction profiles which can be too fast to fill large mold sizes before gelation begins to initiate. Attempts to continue injection of such polymer forming ingredients into a mold after gel results in poor polymer flow causing rapid and excessive tool pressure build-up and the potential for the rupture of the tool. Although an increase in the speed of mixing and delivery of the reaction ingredients into the mold can overcome some of these difficulties, there is a practical limit above which laminar flow will be upset. This will result in voids and unequal distribution of polymer in the mold.
We have now discovered that elastomeric polyurethanepolyurea polymers which are characterized, surprisingly, by good hardness, tear, and improved modulus properties and improved demold strengths compared to prior art aromatic diamine extended polyurethanes, can be prepared by using mixed aromatic amine-diol extenders in which the diamine is the minor component. Surprisingly, the polymer-forming reactants have reaction profiles fast enough to be suitable for rapid molding and demolding processes, for example RIM applications, yet slow enough to enable the filling of large mold sizes before gelation can occur and thereby avoid the prior art problems noted above.